The present invention relates to an optical communication card comprising a forward error correction (FEC) function and to an optical transmission device.
Along with the recent popularization of an optical communication technology in various fields such as the Internet (registered trademark) and optical phones, various technologies to realize a long distance transmission and a large-capacity transmission have been developed in an optical transmission system.
As to the long distance transmission, in general, as a propagation distance becomes longer, a data error in a signal propagation due to an influence of a propagation loss in an optical fiber becomes more prominent. Therefore, an error correction function called an FEC function is effective. The FEC is a technology that correction bits necessary for a data correction are inserted into data to be transmitted on a transmission side, an error detection is performed based on the correction bit on a reception side, and when an error is detected, the data is corrected. Even if a data error occurs, the data correction is possible on the reception side without retransmitting data. Retransmission of data is prevented, and speeding up of the data is possible. At present, several types of FECs are widely used, and a generic FEC (GFEC) using an RS [255, 239] code standardized by ITU-T G.709 and an enhanced FEC (GFEC) standardized by ITU-T G.975.1 are typically used By using various codes such as a BCH [3860, 3824] code and an RS [1023, 1007] code gong the EFECs, multiple types of FECs can be realized.
As compared with the conventional GFEC, the EFEC has excellent error correction capability and can suppress an increase in a bit error rate along with an increase in transmission capacity. The conventional GFEC can correct an error up to approximately an error rate of 10−5, and on the other hand, the EFEC can correct an error up to approximately an error rate of 10−3 by performing Concatenated Coding. Here, the error rate represents a percentage of the number of occurring error bits per one hundred thousand bits of transmitted data. The error rate after the error correction in the correctable range of the GFEC and the EFEC is generally an error rate of 10−12 or less requested for a high-speed signal such as fiber channel signal. Note that since the EFEC performs two or more times of error correction calculations, power consumption also increases as a throughput of information increases.
JP-A-2010-118896 discloses a method for suppressing power consumption. JP-A-2010-118896, the number of bit errors of a main signal propagating on an optical transmission line is always monitored, and when the number of bit errors is smaller than the set threshold, an FEC function is not used. Then, the FEC function is necessary when a bit error increases during practical operation, and it is operated. This process permits power consumption of the unnecessary FEC function during practical operation to be reduced.
On the other hand, as to a large capacity, by the multiplexing technology such as me-division multiplexing or wavelength-division multiplexing, an optical transmission system having the transmission capacity of 40 Gbit/s (hereinafter, referred to as “bps”) or 100 Gbps has been developed, recently.
Further, as a technology of performing a path selection by an optical transmission device, there are an optical switching technology of switching large capacity optical signals and a packet switching technology of switching large capacity optical signals on a packet basis. Note that in a current practical technology, when performing a packet switching, it is necessary to convert an optical signal into an electrical signal, to read destination information on each packet basis and to perform the packet switching. Therefore, it is also necessary to speed up a transmission speed of electrical signals in the device. As the transmission speed of electrical signals used in the current packet switching technology, 1 Gbps or 3.125 Gbps is the mainstream. Also, a packet switching element for 6.25 Gbps or up to 11.1 Gbps is currently developed. Since, when an electrical signal propagates through the device, propagation loss is caused by a substrate or connectors, etc., it is necessary to design considering propagation loss and the transmission speed. At present, the standard “10GBASE-KR” in which a backplane (hereinafter, referred to as “BP”) transmission of 10 Gbps is assumed in IEEE802.3ap is standardized including the FEC function, and the standard makes it possible to correct the data error possibly occurring due to the propagation loss and to speed up transmission speed of electrical signals.